As far as I know, there isn't a way for different Alexa accounts to share smart devices, but it can be done at the device level.
Most manufacturers allow sharing of their devices. For example, Wyze cameras and smart bulbs can be shared with other users. Using Wyze app, the 1st user only has to invite a 2nd user to share a device. Then the second user will accept the invite. If the 2nd user does not currently use the Wyze app, they will need to install the app and create an account before being able to accept the invite. The 2nd user should enable the Wyze skill for Alexa and link their account. After that, the 2nd user's Alexa account should be able to see the new (shared) device.
The way this works will be different for every manufacturer of your smart devices. Your starting point should be with the device's app (whether it's Wyze, Wemo, Philips, Kasa, etc.) and see where it leads you.